1. The Field of the Invention
The present invention relates to electrosurgical instruments for alternatively ablating and coagulating tissue in an arthroscopic procedure.
2. The Relevant Technology
Electrosurgical procedures utilize an electrosurgical generator to supply radio frequency (RF) electrical power to an active electrode for cutting and/or coagulating tissue. An electrosurgical probe is generally composed of a metallic conductor surrounded by a dielectric insulator such as plastic, ceramic, or glass. The surface of the electrode remains exposed and provides the cutting or ablating surface. During an electrosurgical procedure, the metal electrode is often immersed in a conducting fluid and is brought in contact with or in close proximity to the tissue structure to be ablated or coagulated. During a procedure, the probe is typically energized at a voltage of a few hundred to a few thousand volts and at a frequency between 100 kHz to over 4 MHz. The voltage induces a current in the conductive liquid, which causes heating. The most intense heating occurring in the region very close to the electrode where the current density is highest.
Depending on how the electrosurgical instrument is configured, the heat generated from the device can be used to coagulate tissue (e.g., cauterize tissue) or alternatively to ablate tissue (i.e., cut tissue). To cause ablation (i.e., cutting), the electrode generates enough heat to form gas bubbles around the electrode. The gas bubbles have a much higher resistance than tissue or saline, which causes the voltage across the electrode to increase. Given sufficient power, the electrode discharges (i.e., arcs). The high voltage current travels through the gas bubbles and creates a plasma discharge. Moving the electrode close to tissue causes the plasma layer to come within a distance sufficiently close to remove or ablate the tissue.
Electrosurgical instruments can also be used for coagulating tissue. In coagulation, the current density at the electrode is configured to cause heating without cutting. The current density is kept sufficiently high to cause proteins and/or other components of the tissue to agglomerate, thereby causing coagulation. However, during coagulation, the electrode's current density is limited to prevent ablation.
Some existing electrosurgical instruments can perform both ablation and coagulation. In most cases, the physician switches between the ablation mode and the coagulation mode by reducing the power from the RF generator. Reducing the power output of the RF generator reduces the current density at the electrode, which prevents the electrode from arcing and generating a plasma. Consequently, the electrosurgical instrument will cause coagulation. Once the physician has completed the desired coagulation, the power of the RF generator can be increased to return to the ablation mode.